Human neutrophil elastase inhibitory dihydrobenzoxanthones and alkylated flavones from the Artocarpus elasticus root barks

Yeong Jun Ban,Ki Hun Park,Jeong Yoon Kim,Mohd Azlan Nafiah,Aizhamal Baiseitova

doi:10.1186/s13765-020-00549-3

Abstract

Neutrophil elastases are deposited in azurophilic granules interspace of neutrophils and tightly associated with inflammatory ailments. The root barks of Artocarpus elasticus had a strong inhibitory potential against human neutrophil elastase (HNE). The responsible components for HNE inhibition were confirmed as alkylated flavones (2–4, IC50 = 14.8 ~ 18.1 μM) and dihydrobenzoxanthones (5–8, IC50 = 9.8 ~ 28.7 μM). Alkyl groups on flavone were found to be crucial functionalities for HNE inhibition. For instance, alkylated flavone 2 (IC50 = 14.8 μM) was 20-fold potent than mother compound norartocarpetin (1, IC50 > 300 μM). The kinetic analysis showed that alkylated flavones (2–4) were noncompetitive inhibition, while dihydrobenzoxanthones (5–8) were a mixed type I (KI < KIS) inhibitors, which usually binds with free enzyme better than to complex of enzyme–substrate. Inhibitors and HNE enzyme binding affinities were examined by fluorescence quenching effect. In the result, the binding affinity constants (KSV) had a significant correlation with inhibitory potencies (IC50).

Highlights

Serine proteases are the largest and most important unit among the enzyme groups found in eukaryotes and prokaryotes, which distinctively increases the reaction of the peptide bonds hydrolysis [1]
One of them the neutrophil elastase (NE, EC 3.4.21.37) 29 kDa chymotripsis family protease, largely expressed by neutrophils precursors inside the bone marrow, in its mature active form they placed in primary granules [2]
The aim of the present study was the investigation of human neutrophil elastase (HNE) inhibitory potential of the root barks of A. elasticus, and to isolate the responsible components for HNE inhibition

Summary

Introduction

Serine proteases are the largest and most important unit among the enzyme groups found in eukaryotes and prokaryotes, which distinctively increases the reaction of the peptide bonds hydrolysis [1]. One of them the neutrophil elastase (NE, EC 3.4.21.37) 29 kDa chymotripsis family protease, largely expressed by neutrophils precursors inside the bone marrow, in its mature active form they placed in primary (azurophilic) granules [2]. Throughout inflammation spread into the cell interspace NE activity closely contained by an abundant blood plasma inhibitor—α1-antytrypsin (AAT) [3]. Single metabolites reported in vivo antimalarial [13], inhibition of LPS-induced inflammation [14], α-glucosidase inhibitory [15], TRAILresistance overcoming with antiviral [16], and anticancer [17] activities. Alkylated flavonoid Artonin E from A. elasticus revealed considerable cytotoxic effect in MCF-7 human breast cancer cells by ROS mediated mitochondrial pathway [18, 19]. Metabolites in A. elasticus has not been reported to have HNE inhibitory potential capacity

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